There has been known a technology in which an on-board unit mounted on a vehicle acquires a current position of the vehicle to estimate a road on which the vehicle is currently travelling on the basis of road information on map data stored in advance. The on-board unit, which is, for example, a car navigation apparatus, uses a GPS, a gyro, a vehicle speed sensor and the like to acquire the current position of the vehicle. For the map data, information stored in a storage medium is used.
As for the map data, viewability for a user when the map is displayed on a display device is prioritized. Accordingly, two or more roads actually overlapping each other in a height direction or two or more roads actually adjacent to each other are stored as the map data so as to have an interspace therebetween. This allows the user to easily recognize the map. However, there are some cases where the current position estimated by the on-board unit does not match the road information on the map data. Therefore, the map matching is performed in estimating the road on which the vehicle is currently travelling. The map matching is the technology for matching the current position of the vehicle with the road information on the map data.
For example, Patent Citation 1 has disclosed a technology in which with respect to a link, of roads in the map data, which has no width and is set at the center of the width of the road, a direction and a distance by which the link is displaced are calculated in accordance with a width of a road parallel to the road, or a positional relationship of both roads to set the link and the map matching threshold.
Patent Citation 1: Japanese Unexamined Patent Application, Publication No. 2008-14666 (paragraphs [0009], [0010], [0025], etc.)